Relective polymeric body

ABSTRACT

A multilayered reflective body which is thermoformable and capable of being fabricated into relatively thick parts while maintaining a uniform reflective appearance is provided. The reflective polymeric body includes at least first and second diverse polymeric materials of a sufficient number of alternating layers of the first and second polymeric materials such that at least 30% of the light incident on the body is reflected. A substantial majority of the individual layers of the body have an optical thickness of at least 0.45 micrometers, and adjacent layers of the first and second polymeric materials differ from each other in refractive index by at least about 0.03. The reflective body may be fabricated into sheets, mirrors, noncorroding metallic appearing articles and parts, reflectors, reflective lenses, and the like.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.07/368,695, Filed June 20, 1989, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a multilayered polymeric body, whichreflects light and which can be fabricated to have a silvery or hued(i.e., copper, gold, etc.) metallic or nonconventional hued (i.e., blue,green, etc.) appearance, and to articles produced therefrom which mayfind use as mirrors, reflectors, lenses, polarizers, and the like.

Conventional methods for fabricating reflective surfaces include formingsuch surfaces of highly polished metals. Because of the high costs andfabricating problems involved in using metals, more recently fabricatorshave used plastic surfaces which contain thin coatings of metal thereon.Thus, metal coated plastic articles are now commonly found as bothdecorative and functional items in a number of industries. Such articlesare used as bright work for consumer appliances such as refrigerators,dishwashers, washers, dryers, radios, and the like. These types ofarticles are also used by the automotive industry as head lampreflectors, bezels, radio knobs, automotive trim, and the like.

Typically, such metal coated plastic articles are formed byelectroplating or by the vacuum, vapor, or chemical deposition of a thinmetal layer on the surface of the article. Additionally, such coatingsare subject to the chipping and flaking of the metal coatings as well ascorrosion of the metal over time. If additional protective layers mustbe applied over the metal coating to protect it, additional labor andmaterials costs are involved. Further, there may be environmentaldisposal problems with some metal deposition processes.

Multilayer articles of polymers are known, as are methods andapparatuses for making such articles. For example, such multilayeredarticles may be prepared utilizing multilayer coextrusion devices asdescribed in commonly-assigned U.S. Pat. Nos. 3,773,882 and 3,884,606 toSchrenk. Such devices are capable of simultaneously extruding diversethermoplastic polymeric materials in substantially uniform layerthicknesses. The number of layers may be multiplied by the use of adevice as described in commonly-assigned U.S. Pat. No. 3,759,647 toSchrenk et al.

Im et al, U.S. Pat. No. 4,540,623, Teach a multilayer laminated articlewhich includes a polycarbonate as one of the alternating layers. Thearticles of Im et al, however, are intended to be transparent ratherthan reflective and to exhibit optical properties comparable to a purepolycarbonate polymer.

Alfrey, Jr. et al, U.S. Pat. No. 3,711,176, teach a multilayered highlyreflective thermoplastic body fabricated using thin film techniques.That is, the reflective thin film layers of Alfrey, Jr. et al relied onthe constructive interference of light to produce reflected visible,ultraviolet, or infrared portions of the electromagnetic spectrum. Suchreflective thin films have found use in decorative items because of theiridescent reflective qualities of the film.

However, the films of Alfrey, Jr. et al. are extremely sensitive tothickness changes, and it is characteristic of such films to exhibitstreaks and spots of nonuniform color. Further, color reflected by suchfilms is dependent on the angle of incidence of light impinging on thefilm. Thus, such films are not practical for uses which requireuniformity of reflectivity. Moreover, such films are not practical tothermoform into articles as localized thinning of the layers duringthermoforming causes alterations in the reflective characteristics ofthe films.

Accordingly, there remains a need in the art for a polymeric reflectivesheet or body which can be fabricated into relatively thick partswithout alteration of the uniform reflective appearance of the materialover a range of processing conditions and part geometry. Further, thereis a need for a reflective polymeric sheet or body which can be postformed without alteration of the uniform reflective appearance of thematerial. Still further, there is a need for silvery or metallicappearing articles which do not use metal.

SUMMARY OF THE INVENTION

The present invention meets those needs by providing a multilayeredpolymeric reflective body which is post formable and capable of beingfabricated into relatively thick parts while maintaining a uniformhighly reflective appearance. The terms "reflective", "reflectivity","reflection", and "reflectance" as used herein refer to totalreflectance (i.e., ratio of reflected wave energy to incident waveenergy) sufficiently specular in nature such that the polymeric body hasa metallic appearance. The use of these terms is intended to encompasssemi-specular or diffuse reflection such as that of brushed metal,pewter, and the like. In general, reflectance measurement refers toreflectance of light rays into an emergent cone with a vertex angle of15 degrees centered around the specular angle.

A specific intensity of reflectance, when used herein, is the intensityof reflection which occurs at a wavelength where negligible absorptionoccurs. For example, a silver appearing article reflects substantiallyall visible wavelengths, whereas the introduction of a dye to achieveother metallic hues will necessarily lower reflectivity the body at theabsorbing wavelengths. Wavelengths unaffected by the dye will bereflected at essentially the same intensity as a non-dyed sample, and itis at these unaffected wavelengths to which the intensity of reflectionis referring.

According to one aspect of the present invention, a reflective polymericbody of at least first and second diverse polymeric materials isprovided, the body comprising a sufficient number of alternating layersof the first and second polymeric materials such that at least 30% oflight incident on the body is reflected. As used herein, the term"light" is meant to encompass not only visible light but alsoelectromagnetic radiation in both the infrared and ultraviolet regionsof the spectrum. The term "at least 30% of light incident on the body"refers, as discussed above, to reflected light at wavelengths wherenegligible absorption occurs.

A substantial majority of the individual layers of the body have anoptical thickness of at least 0.45 micrometers, and preferably at least75% of the individual layers have at least this optical thickness orgreater. Alternatively, the individual layers should have an opticalthickness such that no visibly perceived iridescence is reflected fromthe body. The first and second polymeric materials differ from eachother in refractive index by at least about 0.03.

A number of substantially transparent polymers are suitable for use inthe present invention. In a preferred embodiment of the invention, thefirst polymeric material is polycarbonate or rigid or flexiblepolyurethane and the second polymeric material is polymethylmethacrylate or polyether amide. The polymeric body may also comprisethree or more alternating layers of diverse polymeric materials. In oneembodiment using a three layer pattern of repeating units ABCBA, thefirst (A) polymeric material is polystyrene, the second (B) material isa styrene-hydroxy ethylacrylate copolymer, and the third (C) polymericmaterial is polymethyl methacrylate. Alternatively, the first and thirdmaterials may be the same, and the second (B) material may be acopolymer of styrene and methyl-methacrylate.

For some three layer combinations, the B layer may not only contributeto the reflective properties of the body but may also act as an adhesivelayer to bond the A and C layers in the multilayer body. It is notnecessary that the refractive index mismatch of the B layer with theother two layers be at least about 0.03. For example, the refractiveindex of the polymer making up the B layer may be intermediate that ofthe A and C layers.

Other three layer repeating patterns are also possible. For example, anABCABC repeating pattern may be used where the polymer making up thethird polymer layer may be placed in the multilayer body as a moistureor oxygen barrier layer or toughening layer. When the third polymerlayer is a barrier layer, it may be present as a single layer on one orboth exterior surfaces of the body or as an interior layer. For example,suitable barrier layer materials such as hydrolyzed ethylene vinylacetate, copolymers of polyvinylidene chloride, nitrile polymers, andnylons may be used in or on the multilayer body. Suitable adhesivematerials such as maleic anhydride grafted polyolefins may be used tobond such barrier layer materials to the multilayer body.

Also, the third polymer layer may be found as a surface or skin layer onone or both major exterior surfaces for an ABABAB repeating body or asan interior layer. The skin layer may be sacrificial, or may bepermanent and serve as scratch resistant or weatherable protectivelayer. Further, such skin layers may be post applied to the body aftercoextrusion. For example, a skin layer may be applied as a sprayed oncoating which would act to level the surface of the body to improveoptical properties and impart scratch resistance, chemical resistanceand/or weatherability. The skin layer may also be laminated to themultilayered body. Lamination is desirable for those polymers which arenot readily coextrudable.

In certain embodiments of the invention, it is desirable to form thereflective polymeric body to comprise at least 500 or more layers.Increasing the number of layers in the polymeric body has been found toincrease its reflectivity (i.e., the percentage of incident lightreflected from the body). Thus, by controlling the number of layers, thedegree of reflectivity of the article may be controlled.

In some embodiments of the invention it may be desirable to incorporatecoloring agents such as dyes or pigments into one or more of theindividual layers of the polymeric body. This can be done to one or bothof the outer or skin layers of the body, or alternatively, the coloringagent may be incorporated into one or more interior layers in the body.The coloring agents may be selected to give the polymeric body ametallic appearance other than its normal silvery appearance such asbronze, copper, or gold, for example.

Different colors such as black, blue, red, yellow, white, and the likemay also be used. Typically, it is most desirable to use pigmentedcoloring agents in the interior layers to provide opaqueness and atwo-sided mirror-like reflective quality and to use dyes on exteriorsurface layers. Coloring agents may be used in combination to providedesirable coloring and optical properties. For example, a pigmentedwhite coloring agent may be used in an interior surface while a coloreddye, such as blue, yellow,red, or green may be included on one or moresurface layers to provide a unique reflective colored effect.

Further, while the normal surface of the body is smooth to give a highlyreflective silver appearance, in some instances it may be desirable togive the surface of the body a roughened or brushed appearance tosimulate a brushed metallic appearance. Further, a solvent may be usedto etch the surface of the multilayer body to provide a matte or pewterlook to the body. Additionally, the body may be embossed with a varietyof patterns to provide desirable optical effects.

The reflective polymeric body of the present invention may find severalapplications. In another embodiment of the invention, the reflectivebody may be fabricated as a mirror-like polymeric article having atleast first and second major surfaces, the article comprising asufficient number of alternating layers of first and second polymericmaterials such that at least 30% of the light incident on the article isreflected. A substantial majority of the individual layers of thearticle have an optical thickness of at least 0.45 micrometers, whilethe first and second polymeric materials differ from each other inrefractive index by at least about 0.03.

To provide the mirror-like quality to the article, one of the majorsurfaces includes a light absorbent layer, such as a layer of a black orother colored pigment. The light absorbent layer may be coextruded orapplied as a lacquer or paint. Alternatively, increasing the number ofindividual layers to above 500 or more results in increased reflectanceof incident light from the article resulting in a mirror-like quality inthe article.

The reflective polymeric body of the present invention may also befabricated to appear mirror-like on all major surfaces by coextruding alight absorbing layer in the interior of the article. Thus, amirror-like polymeric article is provided which has at least first andsecond major surfaces, with the article comprising a sufficient numberof alternating layers of first and second polymeric materials such thatat least 30% of light incident on the article is reflected and at leastone interior light absorbing layer. A substantial majority of theindividual layers of the article have an optical thickness of at least0.45 micrometers, while the first and second polymeric materials differfrom each other in refractive index by at least about 0.03.

The reflective polymeric body of the present invention may also befabricated to act as a birefringent light polarizer which polarizes abroad band of the electromagnetic spectrum. The polarizer is fabricatedof at least first and second diverse polymeric materials, with thepolarizer comprising a sufficient number of alternating layers of thefirst and second polymeric materials such that at least 30% of lightincident on the polarizer is reflected in the plane of polarization. Asubstantial majority of the individual layers of the polarizer have anoptical thickness of at least 0.45 micrometers, with the first andsecond polymeric materials differing from each other in refractive indexby at least about 0.03 in one plane of the polarizer. In a preferredembodiment, the difference in refractive index between the first andsecond polymeric materials is caused by selecting polymers havingdiffering stress optical coefficients and then stretching thosematerials in a uniaxial direction to orient the polymeric materials.

Additionally, the multilayer reflective polymeric bodies of the presentinvention may be formed into a number of decorative and/or structuralparts. The bodies may be formed by coextrusion techniques initially intosheets which may then be post formed. Such post forming operations mayinclude thermoforming, vacuum forming, or pressure forming. Further,through the use of forming dies, the multilayer reflective body may beinitially formed into a variety of useful shapes including profiles,tubes, parisons which can then be formed into blow-molded containers,and the like.

Accordingly, it is an object of the present invention to provide areflective polymeric body which can be fabricated into relatively thickparts, is post formable, and which has a uniformly reflectiveappearance. This, and other objects and advantages of the invention willbecome apparent from the following detailed description, theaccompanying drawing, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b show the relationship among percent reflection of light,difference in refractive index (ΔN), and number of layers for a twocomponent system of polymers made in accordance with the presentinvention. The relationship holds true for any two component system.Further, while the plot goes up to 5000 layers and up to a refractiveindex difference of 0.15, it is within the scope of the invention tohave polymeric bodies of greater than 5000 layers and/or refractiveindex differences of greater than 0.15.

FIG. 2 is a schematic cross-section of a two component multilayerpolymeric reflective body of the present invention, where the firstpolymer has a refractive index, n₁, and the second polymer has arefractive index, n₂.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a highly reflective multilayer polymericbody made up of from a hundred to several thousand alternating thicklayers of polymers which differ from each other in refractive index. Asubstantial majority of the individual layers of the polymeric materialshave an optical thickness of at least 0.45 micrometers or greater, wherethe optical thickness is defined as the product of the individual layerthickness times the refractive index of the polymeric material whichmakes up that layer. Preferably, the individual layers which make up themultilayer body are substantially continuous.

Thus, the multilayer reflective polymeric body of the present inventionis made up of multiple alternating thick layers, as opposed to themultilayer "thin film" articles of the prior art. For purposes ofoptical properties, i.e., reflectance and transmittance, a thin film canbe described as a film thinner than one wavelength of light at which thefilm will be applied. Thus, for films to be used in the visiblewavelength band, a thin film is described in the literature as one whosethickness, D, is less than about 0.5 micrometer or whose opticalthickness, ND (where N is the refractive index of the material) is lessthan about 0.7 micrometers. Vasicek, Optics of Thin Films (1960) atpages 100 and 139.

Prior art thin film layer articles describe interference films whichrely on the constructive optical interference of light to produceintense reflected coherent light in the visible, ultraviolet, orinfrared portions of the electromagnetic spectrum according to theequation:

    λ.sub.m =(2/m) (N.sub.1 D.sub.1 +N.sub.2 D.sub.2),

where λ_(m) is the reflected wavelength in nanometers, N₁ and N₂ are therefractive indices of the alternating polymers, D₁ and D₂ are thethickness of the respective layers of polymers in nanometers, and m isthe order of reflection (m=1,2,3, . . . ). Each solution of the equationdetermines a wavelength at which an intense reflection, relative tosurrounding regions, is expected. The intensity of the reflection is afunction of the "f-ratio" where,

    f=N.sub.1 D.sub.1 /(N.sub.1 D.sub.1 +N.sub.2 D.sub.2)

By proper selection of the f-ratio, one can exercise some degree ofcontrol over the intensity of reflection of the various higher orderreflections. For example, first order visible reflections of blue (0.38micrometer wavelength) to red (0.68 micrometer wavelength) can beobtained with layer optical thicknesses between about 0.075-0.25micrometers. Iridescent films may also be designed to reflect visiblelight at higher order reflectances, although at lower intensities.

As can be seen, such thin film polymeric bodies are strongly dependentupon film (and individual layer) thickness to determine reflectedwavelength. Such thin films are extremely sensitive to thicknesschanges, and it is characteristic of such thin films to exhibitnonuniform streaks and spots of color.

The multilayer bodies of the present invention do not display vividiridescence. In fact, it is an important object of this inventionspecifically to avoid layer thicknesses which result in substantialiridescent color. By keeping all layers sufficiently thick, higher orderreflections are so closely spaced that the human eye perceives thereflection to be essentially silver and non-iridescent.

Articles made in accordance with the present invention exhibit a uniformsilvery reflective appearance, not the multicolored, iridescentappearance common to prior art thin film multilayer articles. Rather,the reflective characteristics of the multilayer bodies of the presentinvention are governed by the following equation:

    R=(kr)/(1+(k-1)r) x 100,

where R is the amount of reflected light (%), k is the number of thickfilm layers, and r=[(N₁ -N₂)/(N_(1+N) ₂)]². See Vasicek, Optics of ThinFilms (1960) at pages 69-70.

This equation indicates that the intensity of the reflected light, r, isa function only of r and k, where r and k are defined as above. As aclose approximation, R is a function only of the refractive indexmismatch of the two polymer components and the total number of layerinterfaces. This relationship contrasts greatly with that of prior thinfilm articles whose reflectivity is highly sensitive to layer thicknessand angle of view.

Thus, the reflected wavelength of light from the multilayer polymericbody of the present invention is independent of both individual layerand total structure thickness over a wide processing range so long as asubstantial majority of the individual layers has an optical thicknessequal to or greater than about 0.45 micrometers. Uniformity ofreflection is inherent in the design of the body. Moreover, a gradientof layer thickness through the thickness of the body is neitherdetrimental nor advantageous to the appearance of the body as long as asubstantial majority of the individual layers of the polymers maintainsan optical thickness equal to or greater than about 0.45 micrometers.This again contrasts with prior thin film articles which reflect broador narrow bandwidths depending upon layer thickness gradient.

Thus, it is not necessary for all of the layers in the reflectivepolymeric bodies of the present invention to have optical thicknesses of0.45 micrometers or greater. The preferred coextrusion process forfabricating the polymeric bodies of the present invention may introducelayer thickness variations both through the thickness of the body and inthe plane of individual layers. Variation in layer thicknesses of eachpolymeric component can be as much as 300% or more. However, usefulreflective bodies and articles may be made even with such widevariations as long as a substantial majority of the layers have anoptical thickness of at least 0.45 micrometers. With this condition met,there is an absence of visibly perceived interference colors reflectedfrom bodies and articles of the present invention.

The absence of the iridescent interference colors which characterizeprior art thin films is somewhat subjective to the human eye. However,we have found that about 75% of the layers in the body must have opticalthicknesses greater than 0.45 micrometers to obtain the broad band,visually uniform reflectance of substantially all wavelengths (whitelight) which characterizes the present invention. A minority of about25% or fewer of the layers having optical thicknesses of less than 0.45micrometers have been found to have interference reflections of asufficiently low intensity so that the body will have essentially novisibly perceived iridescence.

The reflective polymeric bodies of the present invention become morehighly reflective of incident light (i.e., transmit less light) as thenumber of layers is increased. Preferably, the number of layers issufficient to produce an article which will reflect at least 30% of theincident light, for those wavelengths for which there is negligibleabsorption. Reflectances below about 30% are not sufficient to bereadily observed. If it is desired to use the reflective polymeric bodyof the present invention as a mirror, adding additional layers willincrease the reflectance of the body to 50% or higher to produce asilvery, mirror-like appearance.

The reflectivity of the bodies is also dependent upon the difference inrefractive index between the two polymers used. That is, the greater thedifference in refractive index, the greater the reflectivity of thebody. Accordingly, it can be seen that the reflective nature of thepolymeric bodies may be controlled by the selection of polymers havingdiffering refractive indices and by fabricating the body to haveadditional layers. The relationship between percent reflection of light,difference in refractive index (ΔN), and number of layers of material isillustrated in FIGS. 1a and 1b for a two component system.

A typical two component multilayer refelective polymer body 10 is shownschematically in FIG. 2. The body 10 includes alternating layers offirst polymer 12 having a refractive index, n₁, and a second polymer 14having a refractive index, n₂. A substantial majority of the individuallayers have an optical thickness of at least about 0.45 micrometers.

The reflective multilayered polymeric bodies of the present inventionmay comprise alternating layers of a wide variety of generallytransparent thermoplastic materials. Suitable thermoplastic resins,along with representative refractive indices, which may be used in thepractice of the present invention include, but are not limited to:perfluoroalkoxy resins (refractive index=1.35), polytetrafluoroethylene(1.35), fluorinated ethylene-propylene copolymers (1.34), siliconeresins (1.41), polyvinylidene fluoride (1.42),polychlorotrifluoroethylene (1.42), epoxy resins (1.45), poly(butylacrylate) (1.46), poly(4-methylpentene-1) (1.46), poly(vinyl acetate)(1.47), ethyl cellulose (1.47),polyformaldehyde (1.48), polyisobutylmethacrylate (1.48), polymethyl acrylate (1.48), polypropyl methacrylate(1.48), polyethyl methacrylate (1.48), polyether block amide (1.49),polymethyl methacrylate (1.49), cellulose acetate (1.49), cellulosepropionate (1.49), cellulose acetate butyrate (1.49), cellulose nitrate(1.49), polyvinyl butyral (1.49), polypropylene (1.49), polybutylene(1.50), ionomeric resins such as Surlyn (trademark) (1.51), low densitypolyethylene (1.51), polyacrylonitrile (1.51), polyisobutylene (1.51),thermoplastic polyesters such as Ecdel (trademark) (1.52), naturalrubber (1.52), perbunan (1.52), polybutadiene (1.52), nylon (1.53),polyacrylic imides (1.53), poly(vinyl chloro acetate) (1.54), polyvinylchloride (1.54), high density polyethylene (1.54), copolymers of methylmethacrylate and styrene such as Zerlon (trademark) (1.54), transparentacrylonitrile-butadiene-styrene terpolymer (1.54), allyl diglycol resin(1.55), blends of polyvinylidene chloride and polyvinyl chloride such asSaran resins (trademark) (1.55), polyalpha-methyl styrene (1.56),styrene-butadiene latexes such as Dow 512-K (trademark) (1.56),polyurethane (1.56), neoprene (1.56), copolymers of styrene andacrylonitrile such as Tyril resin (trademark) (1.57), copolymers ofstyrene and butadiene (1.57), polycarbonate (1.59), other thermoplasticpolyesters such as polyethylene terephthalate and polyethyleneterephthalate glycol (1.60), polystyrene (1.60), polyimide (1.61),polyvinylidene chloride (1.61), polydichlorostyrene (1.62), polysulfone(1.63), polyether sulfone (1.65), and polyetherimide (1.66). Therefractive indices reported above may vary somewhat at differentwavelengths. For example, the refractive index of polycarbonate issomewhat greater for light in the blue region of the spectrum andsomewhat lower for light in the red region of the spectrum.

Copolymers of the above resins are also useful such as ethylene andvinyl alcohol, styrene and hydroxy ethylacrylate, styrene and maleicanhydride, styrene-butadiene block copolymers, styrene andmethlymethacrylate, and styrene and acrylic acid. Other useful polymericmaterials include polyetheretherketones, polybutene, maleic anhydridegrafted polyolefins such as Admer (available from Mitsui Chemicals) andPlexar (available from Quantum Chemicals), and copolymers of ethyleneand vinyl acetate such as CXA (available from du Pont). The latter threepolymers are particularly useful as adhesive layers to bond otherpolymeric layers together in the multilayer construction.

A condition for the selection of the polymers to make up the alternatinglayers of the body is that the polymers selected have refractive indiceswhich differ from each other by at least about 0.03. Further, thepolymers should be compatible in processing temperatures so that theymay be readily coextruded.

Multilayer bodies in accordance with the present invention are mostadvantageously prepared by employing a multilayered coextrusion deviceas described in U.S. Pat. Nos. 3,773,882 and 3,884,606 the disclosuresof which are incorporated herein by reference. Such a device provides amethod for preparing multilayered, simultaneously extruded thermoplasticmaterials, each of which are of a substantially uniform layer thickness.Preferably, a series of layer multiplying means as are described in U.S.Pat. No. 3,759,647 the disclosure of which is incorporated herein byreference may be employed.

The feedblock of the coextrusion device receives streams of the diversethermoplastic polymeric materials from a source such as a heatplastifying extruder. The streams of resinous materials are passed to amechanical manipulating section within the feedblock. This sectionserves to rearrange the original streams into a multilayered streamhaving the number of layers desired in the final body. Optionally, thismultilayered stream may be subsequently passed through a series of layermultiplying means in order to further increase the number of layers inthe final body.

The multilayered stream is then passed into an extrusion die which is soconstructed and arranged that streamlined flow is maintained therein.Such an extrusion device is described in U.S. Pat. No. 3,557,265, thedisclosure of which is incorporated by reference herein. The resultantproduct is extruded to form a multilayered body in which each layer isgenerally parallel to the major surface of adjacent layers.

The configuration of the extrusion die can vary and can be such as toreduce the thickness and dimensions of each of the layers. The precisedegree of reduction in thickness of the layers delivered from themechanical orienting section, the configuration of the die, and theamount of mechanical working of the body after extrusion are all factorswhich affect the thickness of the individual layers in the final body.It is necessary, however, that the optical thickness of a substantialmajority of the individual layers of polymeric material be at least 0.45micrometers.

Reflective polymeric bodies produced by the practice of the presentinvention may have a wide variety of potentially useful applications.For example, the bodies may be post formed into concave, convex,parabolic, half-silvered, etc. mirrors. If suitably flexible or rubberypolymers (elastomers) are utilized, the bodies may be bent orrecoverably stretched into varying shapes. The mirror-like appearancemay be accomplished by coextruding a black or otherwise light absorbinglayer on one side of the body. Alternatively, one side of the final bodymay be coated with a colored paint or pigment to provide a highlyreflective mirror-like body. Such mirrors would not be subject tobreakage as would glass mirrors.

In some embodiments of the invention it may be desirable to incorporatecoloring agents such as dyes or pigments into one or more of theindividual layers of the polymeric body. This can be done to one or bothof the outer or skin layers of the body, or alternatively, the coloringagent may be incorporated into one or more interior layers in the body.The coloring agents may be selected to give the polymeric body ametallic appearance other than its normal silvery appearance such asbronze, copper, or gold, for example.

Different colors such as black, blue, red, yellow, white, and the likemay also be used. Typically, it is most desirable to use pigmentedcoloring agents in the interior layers to provide opaqueness and amirror-like reflective quality and to use dyes on exterior surfacelayers. Coloring agents may be used in combination to provide desirablecoloring and optical properties. For example, a pigmented white coloringagent may be used in an interior surface while a colored dye, such asblue, yellow,red, or green may be included on one or more surface layersto provide a unique reflective colored effect.

Further, while the normal surface of the body is smooth to give a highlyreflective silver appearance, in some instances it may be desirable togive the surface of the body a roughened or brushed appearance tosimulate a brushed metallic appearance. Further, a solvent may be usedto etch the surface of the multilayer body to provide a matte or pewterlook to the body. Additionally, the body may be embossed with a varietyof patterns to provide desirable optical effects.

The reflective polymeric bodies may also be used as birefringentpolarizers. Through proper selection of the polymeric materials makingup the layers, a refractive index mismatch in one plane of the polarizermay be achieved. In a preferred method, the refractive index mismatchmay be created after fabrication of the reflective polymeric body. Thepolymeric materials may be selected so that the first material has apositive stress optical coefficient and the second polymeric materialhas a negative stress optical coefficient. Stretching the bodycontaining the two polymeric materials in a uniaxial direction causesthem to orient and results in a refractive index mismatch in the planeof orientation to produce the polarizer. A broad band width of visiblelight passing through such bodies is polarized. This is in distinctionto prior thin film multilayer polarizers which polarized only specificnarrow wavelength ranges of light.

Additionally, the highly reflective polymeric bodies may be fabricatedas non-corroding metallic appearing articles for indoor or outdoorexposure. For example, the polymeric bodies may be fabricated intosigns, or bright work for appliances. The bodies may be post formed intohighly reflective parts such as automotive head lamp reflectors, bezels,hub caps, radio knobs, automotive trim, or the like, by processes suchas thermoforming, vacuum forming, shaping, rolling, or pressure forming.The bodies may also be formed into silvery or metallic appearingbathroom or kitchen fixtures which do not corrode or flake.

A number of different profiles may be coextruded in addition to sheetsand films of the reflective polymeric materials. By profiles, we meanshaping of the multilayer body 1) in a forming die into sheets,channels, lenticular cross-sections, round or elliptical tubes, andparisons, or 2) outside of a die by a post forming procedure. Forexample, decorative moldings such as wall moldings and picture framemoldings, automotive trim, home siding, and the like may be readilycoextruded through forming dies. Use of a tubular extrusion die producesa multilayered metallic appearing pipe. Such tubular dies may also beused to produce parisons which may then be blow molded into silveryappearing bottles and containers. Because the materials used in theconstruction of the body may be selected for given desired properties,the final body may be flexible or rubbery, producing an article whichcould be used as a variable focal length reflector by flexing thearticle to different degrees.

The reflective polymeric bodies of the present invention may also bepost formed into a wide variety of items such as two-way mirrors, blackbodies for insulation, and solar intensifiers to concentrate solarradiation. The bodies may also be formed into dinnerware, tableware,containers, and packages. By the proper selection of the polymers whichwere used, such articles may be made to be microwavable.

In order that the invention may be more readily understood, reference ismade to the following examples, which are intended to be illustrative ofthe invention, but are not intended to be limiting in scope.

EXAMPLE 1

Employing an apparatus as generally described in U.S. Pat. Nos.3,773,882 and 3,759,647, a sheet of a reflective polymeric body wasprepared. The sheet was approximately 0.05 inches in thickness and had657 alternating layers (ABABAB) of polycarbonate (Calibre 300-22,trademark of Dow Chemical Company) and polymethyl methacrylate (CyroAcrylite H15-003, trademark of Cyro Industries). A substantial majorityof the layers in the final sheet had optical thicknesses of at least0.45 micrometers. The refractive index of the polycarbonate (PC) was1.586, while the refractive index of the polymethyl methacrylate (PMMA)was 1.49.

The polycarbonate and polymethyl methacrylate materials were heatplastified in extruders maintained at between about 500 and 520 degreesF and fed to a feedblock at a rate of about 20 pounds per hour toproduce the multilayered core of the construction. Another extrudersupplied outer skin layers of polycarbonate to the sheet at the rate ofabout 10 lb/hr. The resulting construction was spread in a coat hangerstyle die (width=16 inches, die gap=0.05 inches) and cooled on a threeroll sheet stack in an "S-rap" configuration.

Portions of the sheet were then thermoformed into various shapes such asreflective lenses, eating utensils, automotive emblems, and other itemsof complex geometry. Some of the shaped items were further enhanced byspray painting one side thereof a flat black color. This resulted in anintense silvery mirror-like appearance when the item was viewed from theopposite side. Additional portions of the sheet were stacked in sevenplies and then heated under pressure to obtain an article having an evengreater number of layers (i.e., 7×657). This resulted in a highlyreflective article which required no painting with a black color toobtain a silvery, mirror-like appearance.

EXAMPLE 2

Using the same apparatus and polymers as in Example 1, a reflectivemultilayer body having 1313 alternating core layers was coextruded. Thepolycarbonate was fed to the extrusion die at a rate of about 32.5 lb/hrand the polymethyl methacrylate was fed a rate of about 17.5 lb/hr.Polycarbonate skin layers were fed at a rate of about 12.5 lb/hr. Areflective sheet was produced in which a substantial majority of thelayers had an optical thickness of at least 0.45 micrometers. Noiridescent color was observed.

EXAMPLE 3

Using the same apparatus and polymers as in Example 1, a reflectivemultilayer body having 1313 alternating core layers was coextruded. Thepolycarbonate was fed to the extrusion die at a rate of about 42.5 lb/hrand the polymethyl methacrylate was fed a rate of about 7.5 lb/hr.Polycarbonate skin layers were fed at a rate of about 12.5 lb/hr. Areflective sheet was produced in which a substantial majority of thelayers had an optical thickness of at least 0.45 micrometers. Noiridescent color was observed.

EXAMPLE 4

Three component reflective polymeric bodies having an ABCBA repeatinglayer pattern were produced using: as the "A" layer, Dow Styron 685Dpolystyrene (specific gravity 1.04; refractive index 1.586); as the "B"layer, Richardson RPC-440 styrene- methylmethacrylate copolymer(specific gravity 1.13; refractive index 1.53); and as the "C" layer,Cyro Acrylite H15-003 polymethyl methacrylate (specific gravity 1.20;refractive index 1.49). The reflective body had 1313 layers ofapproximately equal average thickness (i.e., each of the layers A:B:C:Bmade up 25% of the core). Mass flow rates to theextruders was 9.3 lb/hrfor the polystyrene (PS), 21.0 lb/hr for the styrene-methylmethacrylatecopolymer (SMMA), and 11.7 lb/hr for the polymethyl methacrylate (PMMA).The body included a skin layer of polystyrene (Dow Styron 685D) extrudedat a mass. flow rate of approximately 12.0 lb/hr. A reflective sheet wasproduced in which a substantial majority of the layers had an opticalthickness of at least 0.45 micrometers. No iridescent color wasobserved.

EXAMPLE 5

A three component reflective body was produced as in Example 4 exceptthat the layer thickness ratio was 33:16.7:33:16.7 (A:B:C:B % of thetotal core layers). Extruder rates of 16.7 lb/hr for the PS, 15.0 lb/hrfor the SMMA, and 16.0 lb/hr for the PMMA were used. A reflective sheetwas produced in which a substantial majority of the layers had anoptical thickness of at least 0.45 micrometers. No iridescent color wasobserved.

EXAMPLE 6

A three component reflective body was produced as in Example 4 exceptthat the layer thickness ratio was 41.0:8.6:41.8:8.6 (A:B:C:B % of thetotal core layers). Extruder rates of 25.6 lb/hr for the PS, 22.0 lb/hrfor the SMMA, and 30.0 lb/hr for the PMMA were used. A reflective sheetwas produced in which a substantial majority of the layers had anoptical thickness of at least 0.45 micrometers. No iridescent color wasobserved.

EXAMPLE 7

In order to determine at what point thin layer optical thicknessinterference effects become pronounced, each of the reflective samplesprepared in Examples 1-6 above were tested by heating and stretchingthem through iridescence to the point of transparency. All of thesamples were then visually inspected and measured to determine: 1) totalsample thickness at which a first order reflected blue band wasobserved, and 2) total sample thickness at which little color wasobserved and the sample displayed substantially uniform silveryreflectance. Average individual layer thickness for each component wasthen calculated from known relative compositions of the core and skinlayers as measured by microscopy.

The calculated thicknesses were then multiplied by the respectiverefractive indices of the components to obtain values for opticalthickness. The results are compared to theoretically calculated opticalthickness in Table I below.

                                      TABLE 1                                     __________________________________________________________________________                         EX-        1st ORDER BLUE 1st ORDER BLUE                                      AM-                                                                              COM-    THEORETICAL    MEASURED-CALCULATED                          SAMPLE #                                                                             PLE                                                                              POSITION                                                                              (optical thickness, um)                                                                      avg. (optical thickness,                                                      um)                            __________________________________________________________________________    2 COMPONENT                     PC     PMMA    PC      PMMA                   PC:PMMA       C8801020-35-C                                                                        1  50:50   0.008  0.002   0.141   0.133                                C8900103-19-B                                                                        2  65:35   0.127  0.064   0.114   0.058                                C8900103-17-B                                                                        3  85:15   0.163  0.027   0.167   0.028                  3 COMPONENT                     PS SMMA                                                                              PMMA                                                                              SMMA                                                                              PS  SMMA                                                                              PMMA                                                                              SMMA               PS:SMMA:PMMA:SMMA                                                                           C8900103-29-A                                                                        4  25:25:25:25                                                                           0.048                                                                            0.047                                                                             0.046                                                                             0.047                                                                             0.044                                                                             0.043                                                                             0.042                                                                             0.043                            C8900103-29-B                                                                        5  36:16.7:33:16.7                                                                       0.065                                                                            0.032                                                                             0.061                                                                             0.032                                                                             0.063                                                                             0.031                                                                             0.060                                                                             0.031                            C8900103-31-A                                                                        6  41.0:8.6:41.8:8.6                                                                     0.081                                                                            0.016                                                                             0.076                                                                             0.016                                                                             0.086                                                                             0.017                                                                             0.082                                                                             0.017              __________________________________________________________________________                                                   TRANSISTION TO                                      EX-        5th ORDER BAND UNIFORM REFLECTANCE                                 AM-        THEORETICAL    MEASURED-CALCULATED                          SAMPLE #                                                                             PLE                                                                              COMPOSITION                                                                           (optical thickness, um)                                                                      avg. (optical thickness,                                                      um)                            __________________________________________________________________________    2 COMPONENT                     PC     PMMA    PC      PMMA                   PC:PMMA        C8801020-35-C                                                                       1  50:50   0.45 · 0.85                                                                         0.841   0.790                                C8900103-19-B                                                                        2  65:35   0.45 · 0.85                                                                         1.596   0.808                                C8900103-17-B                                                                        3  85:15   0.45 · 0.85                                                                         3.339   0.560                  3 COMPONENT                     PS SMMA                                                                              PMMA                                                                              SMMA                                                                              PS  SMMA                                                                              PMMA                                                                              SMMA               PS:SMMA:PMMA:SMMA                                                                           C8900103-29-A                                                                        4  25:25:25:25                                                                           0.45 · 0.85                                                                         0.818                                                                             0.789                                                                             0.769                                                                             0.789                            C8900103-29-B                                                                        5  36:16.7:33:16.7                                                                       0.45 · 0.85                                                                         1.745                                                                             0.842                                                                             1.639                                                                             0.842                            C8900103-31-A                                                                        6  41.0:8.6:41.8:8.6                                                                     0.45 · 0.85                                                                         2.442                                                                             0.511                                                                             2.483                                                                             0.511              __________________________________________________________________________

First order blue theoretical was calculated by:

    λ.sub.1 =2× (sum of optical thicknesses of optical repeat unit components)

where, 1=visible blue=0.38 micrometers, and sum of opticalthicknesses=N₁ D₁ +N₂ D₂ for PC:PMMA and =N₁ D₁ +N₂ D₂ +N₃ D₃ +N₂ D₂ forPS:SMMA:PMMA:SMMA

Fifth order band theoretical was calculated by: 5(λ/4)=optical thicknessof minor component where, 0.38 micrometers <λ<0.68 micrometers.

Referring to Table I, it can be seen that there is very good agreementbetween theoretical and measured optical thicknesses for first orderblue reflections and optical thicknesses are in the general range taughtby prior art thin layer iridescent film patents. The measured opticalthicknesses of the transition from very faint iridescent color tosubstantially uniform reflectance of all wavelengths was found to occurwhen the average optical thickness of the minor component was greaterthan about 0.45 micrometers. Disappearance of faint iridescent colorcorrelates very well with the theoretical optical thickness range of theminor component for the fifth order band (0.45 to 0.85 micrometers) asshown in Table I.

While certain representative embodiments and details have been shown forpurposes of illustrating the invention, it will be apparent to thoseskilled in the art that various changes in the methods and apparatusdisclosed herein may be made without departing from the scope of theinvention, which is defined in the appended claims.

What is claimed is:
 1. A reflective polymeric body of first and seconddiverse polymeric materials, the body comprising a sufficient number ofalternating layers of said first and second polymeric materials suchthat at least 30% of light incident on said body is reflected, where theintensity of the reflected light is governed by the equationR=(kr)/(1+(k-1)r)×100, where R is the amount of reflected light (%), kis the number of thick film layers, and r=(N₁ -N₂)/(N₁ +N₂)², and N₁ andN₂ are the refractive indices of said polymeric materials at each layerinterface, a substantial majority of the individual layers of said bodyhaving an optical thickness of at least 0.45 micrometers, and whereinsaid first and second polymeric materials differ from each other inrefractive index by at least about 0.03.
 2. A reflective polymeric bodyof at least first and second diverse polymeric materials, the bodycomprising a sufficient number of alternating layers of said first andsecond polymeric materials such that at least 30% of light incident onsaid body is reflected, but such that essentially no visibly perceivediridescence is reflected, a substantial majority of the individuallayers of said body having an optical thickness of at least 0.45micrometers, and wherein said first and second polymeric materialsdiffer from each other in refractive index by at least about 0.03. 3.The reflective polymeric body of claim 2 in which said first polymericmaterial is polycarbonate and said second polymeric material ispolymethyl methacrylate.
 4. The reflective polymeric body of claim 2 inwhich said first polymeric material is a rigid polyurethane and saidsecond polymeric material is polymethyl methacrylate.
 5. The reflectivepolymeric body of claim 2 in which said first polymeric material is aflexible polyurethane and said second polymeric material is a polyetheramide.
 6. The reflective polymeric body of claim 2 in which said bodycomprises at least 500 layers.
 7. The reflective polymeric body of claim2 in which said polymeric body is thermoformable.
 8. The reflectivepolymeric body of claim 2 including a coloring agent incorporated intoat least one layer of said polymeric body.
 9. The reflective polymericbody of claim 8 in which said coloring agent is selected from the groupconsisting of pigments and dyes.
 10. The reflective polymeric body ofclaim 9 in which said coloring agent is incorporated into at least onesurface layer of said polymeric body.
 11. The reflective polymeric bodyof claim 9 in which said coloring agent is incorporated into at leastone interior layer of said polymeric body.
 12. The reflective polymericbody of claim 2 in which at least one surface layer has a brushed orroughened surface.
 13. The reflective polymeric body of claim 2 in whichat least one surface layer has been etched to provide a matte or pewterfinish.
 14. The reflective polymeric body of claim 2 in which at leastone surface layer has been embossed.
 15. The reflective polymeric bodyof claim 2 in which said first and second polymeric materials areelastomers.
 16. The reflective polymeric body of claim 2 in which atleast 75% of said layers have an optical thickness of at least 0.45micrometers.
 17. The reflective polymeric body of claim 2 in which saidbody is extruded as a profile.
 18. The reflective polymeric body ofclaim 17 in which said body is in the form of a tube.
 19. The reflectivepolymeric body of claim 2 in which said body is post formed into aprofile.
 20. The reflective polymeric body of claim 2 in which said bodyis a blow-molded container.
 21. The reflective polymeric body of claim 2in which said polymeric body is in the form of a sheet having two majorsurfaces.
 22. The reflective polymeric body of claiim 21 in which saidbody includes a permanent protective skin layer on at least one majorsurface thereof.
 23. The reflective polymeric body of claim 2 whichincludes a barrier layer as either an exterior or interior layer of saidbody.
 24. The reflective polymeric body of claim 2 in which saidpolymeric body includes first, second, and third diverse polymericmaterials of alternating layers in a pattern ABCBA.
 25. The reflectivepolymeric body of claim 24 in which said first polymeric material ispolystyrene, said second polymeric material is a styrene hydroxyethylacrylate copolymer, and said third polymeric material is polymethyl methacrylate.
 26. The reflective polymeric body of claim 2 whichincludes a barrier layer as an interior layer of said body.
 27. A mirrorlike polymeric article having at least first and second major surfaces,said article comprising a sufficient number of alternating layers offirst and second polymeric materials such that at least 30% of lightincident on said body is reflected, a substantial majority of theindividual layers of said body having an optical thickness of at least0.45 micrometers, wherein said first and second polymeric materialsdiffer from each other in refractive index by at least about 0.03, andwherein one of said major surfaces includes a light absorbent layer. 28.A mirror like polymeric article having at least first and second majorsurfaces, said article comprising a sufficient number of alternatinglayers of first and second polymeric materials such that at least 30% oflight incident on said body is reflected, and at least one interiorlight absorbing layer, a substantial majority of the individual layersof said body having an optical thickness of at least 0.45 micrometers,and wherein said first and second polymeric materials differ from eachother in refractive index by at least about 0.03.
 29. A birefringentlight polarizer which reflects light anisotropically, comprisingmultiple layers of at least first and second diverse polymericmaterials, a substantial majority of the individual layers of saidpolarizer having an optical thickness of at least 0.45 micrometers, andwherein said first and second polymeric materials differ from each otherin refractive index by at least about 0.03 in one plane of thepolarizer.
 30. The birefringent light polarizer of claim 29 in which thedifference in refractive index between said first and second polymericmaterials is caused by stretching said materials in a uniaxial directionto orient said polymeric materials.